fun word problem..

Good evening Forum , back with another fun fun fun word problem , tell me what you think..
How many liters of a 40% sulfuric acid solution must be mixed with 4 liters of a 24% sulfuric acid solution to produce a 30% solution?

Good evening Forum , back with another fun fun fun word problem , tell me what you think..
How many liters of a 40% sulfuric acid solution must be mixed with 4 liters of a 24% sulfuric acid solution to produce a 30% solution?

Let x be the number of litres of 40% Sulfuric Acid. We're adding x litres of 40%, to 4 litres of 24% to get (x+4) litres of 30%. This can be modelled mathematically by: